The present invention relates to a method of controlling the ignition timing of an internal combustion engine, and more specifically to a method of controlling the ignition timing until the engine is completely warmed-up.
In general, ignition timing of internal combustion engines are retarded until the temperature of the coolant reaches a predetermined value, in order to purify the exhaust gases while the engines are cold. As a result, maximum combustion temperature and thus emission of NOx components decrease; further, the temperature of the exhaust gases increases so that the oxidation of HC components is promoted and the emission thereof is reduced. When the temperature of the coolant reaches a predetermined value, the control for retarding the ignition angle is stopped; the ignition timing is controlled in an ordinary manner, and harmful components are removed by a catalytic converter.
However, the above-mentioned conventional method controls the ignition timing simply relying upon the temperature of the coolant. Therefore, when the engine is started under cold conditions, and even when the control for retarding the ignition is maintained until the temperature of the coolant has reached a predetermined value, the catalytic converter is often not sufficiently warmed-up to its active temperature. In such a case, it is impossible to effectively remove harmful components, especially NOx and HC components that are contained in the exhaust gases.